


Bound

by SinforWin



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Big Sans, Breeding, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), F/M, Possessive Sans, Pregnancy, Rough Sex, Shameless Smut, Smut, Soul Bond, Underfell Sans
Language: English
Status: Completed
Published: 2017-09-08
Updated: 2017-09-08
Packaged: 2018-12-25 01:50:40
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,843
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12025569
Author URL: https://archiveofourown.org/users/SinforWin/pseuds/SinforWin
Summary: Despite all logic, despite the warnings from my family, friends, from my own mind I fell for him. A monsterSin, pure sin and nothing but sin. I feel dirty





	Bound

**Author's Note:**

> why am I doing this?

I sat on my bed cross legged, a kitty pillow locked in my tight grip. From across the room stared back at me a skeleton, the red lights in his eye sockets flickering softly. A cheeky grin on his face occasionally twitched upwards, the golden tooth twinkling in last light of setting sun every time his head, even when only slightly, moved.

I've known Sans for over two years, since he moved from a the town of Ebott with his brother, both wishing to keep away from the place that locked their kind away. Though scared shitless of him at first, I quickly grew fond of his jokes, his words and actions. Over time he became protective of me when necessary, helped me however he could and in return I did the same. It wasn't easy for a large monster, at least, a head taller than most humans to fit in, so I was his comfort. It wasn't easy for a single girl away from everything she was familiar with to grow strong on her own, so he was my support. We soon learned that we needed each other, despite what most people said and thought.  
But after a while my view of him began to shift, my heart would pound harder whenever he was close. Whenever he put his arm on my shoulder or waist to pull me away from someone he didn't like I'd melt never wanting the moment to end. But it always did, and always started anew. I was okay with it, for now that was fine. 

I don't know how I was attracted to a freaking skeleton, let alone falling in love with him, but I never let that distract me. I never told him how I felt, I wasn't ready to. I've never been in a serious relationship and with Sans that's what I'd want it to be. The thought of him being a fleeting moment crushed me. So I kept a straight face, was always careful with my words. And it seems like I was able to hide my feelings, at least that's what I saw, after all he never so much as hinted that he knew or cared.

But the reason he came to me today worried me, the absence of one, to be exact. He just teleported into my bedroom only to stare at me for an hour straight with the creepiest smile he could master. All my questions remained unanswered, so I decided to wait. Doing anything with a feeling of someone's eyes on my back was near impossible, so I stared back in hopes it would annoy him as much as it annoyed me, but he only became more confident with time. 

My patience was growing thin. 

"Sans you have three seconds to either talk or leave" I snapped "I'm sick of you staring and following my ever step. It's fucking creepy"  
A deep chuckle escaped his chest and broke the pose he was keeping like a statue for the past half an hour, if not more. Leaning his both arms on the back of the chair he was seating on, Sans rested his head on top of them, and his eyes instantaneously softened, still fixed on mine.  
"I'm just waitin' sweetheart" he breathed out. 

His voice was deeper than usual, but smoother, calmer. I could listen to it forever.  
"For what?" I raised my brow, not giving a hint of my thoughts.  
"You'll know soon enough" the lights of his eyes disappeared making me flinch. It scared me more than I'd care to admit, from everything I knew he could do and did countless times before, his eyes terrified me the most. I slowly crawled away from him, my back hitting my bed's headboard. I knew he wouldn't hurt me, knew it was part of his thinking process most of the time, but I couldn't help myself.  
He noticed my nervousness, I wasn't exactly hiding it, and he smiled wider. Was he enjoying himself? I lowered my gaze, refusing to show any more fear and it helped. I felt my heart calm.

"There's something I gotta tell ya" he sounded stern, if there was something important he should've told me sooner. I nodded for him to continue without looking up, feeling, somewhat uneasy "I'm leavin' in a week"  
I froze for a moment. As my gaze rose without my command his empty eyes seemed less of a problem. My eyebrows furrowed and I tried to read his expression, as always, unsuccessfully "what are you saying?" a question echoed. Was it me?  
Finding myself on my feet I, slowly but surely, walked up to him, stopping in mere inches "you're kidding right? You can't just leave" my heart was aching. I didn't want this to end. I didn't want us to never be.  
"Well Assgore finished building our first monster town, so I'm moving there" he shrugged as if it was nothing. Didn't it mean anything to him, did I mean nothing? 

I felt my breath stop for a moment, my vision blurring. Was I crying? I rose my hand to wipe away my tears, but he beat me to it. His warm digits grazed over my skin, his palm resting on my cheek "I'm leaving, sweetheart, but don't worry" I saw his grin widen as his arms wrapped around my waist, pulling me closer. He nuzzled his face in my chest and I felt his voice vibrate on my stomach "I'm taking ya with me" 

"W-wait, what?" I wan't sure I heard him right "I... I can't make that kind of decision on a whim. Where would I live?"  
"With me" his one eye opened looking up at me.  
"What about my job?"  
"We'll find ya something new" 

"Why?" I asked after, what it seemed like, forever. His hum spread through my body in a wave of yet another vibration and I remembered that he was still hugging me. I didn't want to pull away, i wanted to treasure those moments. My hands lingered in the air for a moment, hesitant to move, before gently wrapping around his skull. His hand clawed on my back almost possessively and I wondered if I'd be able refuse him, but one question still remained in my mind. 

"Why do you want me to come?"  
"Cause I love you. Cuase you're mine. I'm not letting you go. **E V E R** " he growled his voice layered with a deeper one. His hold on me grew yet stronger, tips of his fingers digging into my back. I whimpered quietly and he gave the spot a gentle stroke.

He loved me. He just said he did. Did I image that? My cheeks heat up and my heartbeat quickened. I couldn't stop myself from smiling. I was happy and it didn't matter whether he meant it or if he lied.

As creepy as it all sounded, as much as my mind told me how wrong this was, I couldn't fight it, I didn't want to. I wanted to go with him, to live by his side all my life, I wanted to be his, forever. And I wanted him to show it. 

_God, what is wrong with me?_

"I... I have to think about it" I whispered, still scared to agree.  
In the darkened room I could no longer see him. I only felt him nod then I heard a deep chuckle. One of his arms traveled down to my thighs and without a warning he stood up, lifting me along with him. I could once again see his eyes, two blood red lights floating softly in the dark. I didn't put up much of a fight, not until I realized what he was doing, but it was too late. Seconds later my back hit the fluffy surface of my bed, his eyes were right in front of mine, his weight was pinning me down. Even though I knew from long ago how big the difference of our strengths was I still tried to push him off. 

_Of course he wouldn't budge_

The red of his eyelights vanished and I felt his teeth over the crook of my neck, ghosting over my skin, before he kissed it again and again, first gently then more demanding.  
"What are you doing, Sans. Stop" I raised my voice, throwing away all the thoughts and senses begging me to let him continue, to let him do whatever he pleased.  
It seemed as if he heard my inner conflict and his advances became bolder. Razor sharp teeth grazed on my shoulder and I shuddered praying for what I suspected to never come. 

He bit down. I thought the pain would overwhelm me, I thought I'd cry out, but all I felt was a weak sting. A strange feeling tugged on my Soul and I gave in to it. My arms shot up, wrapping themselves around his head for the second time. He took it as an acceptance biting harder, in all reality, it was. 

As he pulled away I felt his slick, wet tongue soothing the would he opened. My fingers found their way to my, still slightly stinging, shoulder, but I found it completely healed already. 

"What was that?" I managed to breath out.  
"A mark, love. No one'll dare touch you. You're **m i n e** " a soft whisper reached my ears. Stars, how much I loved it. 

I felt myself nodding and, at that point didn't even try to stop. His confidence must've rocketed, because he proceeded to peppering my neck, shoulders and chest with small kisses. All while his hands ghosted over my skin, advancing up my shirt. I jolted when his fingers brushed against my breasts but it passed in a moment replacing with cold air. I watched him throw my shirt aside, but didn't bother follow its path, my eyes stayed locked at him.

Instinctively my arms locked around my bare chest, but I didn't resist when he pulled them away binding in a tight grip on either side of my head. Nuzzling in my cleavage he kissed every inch of it, as if couldn't get enough. He soon stopped and I felt his teeth on my breast while his hand rubbed the other, now clearly wanting more. I did too. 

My breath hitched when his thumb began to circle around my nipple, occasionally pinching it: strong enough to make me choke on my breath, but not enough to be painful. My fingers tangled around the folds of his jacket, desperate for support. My breath came in short pants, and muffled cries as I tried to hold back moans that threatened to break free every passing second.  
Dragging his crimson tongue over my breast for one last time he let out a dark chuckle. 

"Ya're very obedient, kitten" he laughed tugging on my shorts and panties before discarding them into the darkness of the room "I figured ya liked me, but this much?"  
"A lot" I mumbled closing my eyes. I was too embarrassed to look at him both because of the words and the situation we were in.  
"Ya're lucky then... Cause I wasn't stoppin'" 

I couldn't proceed his words, let alone respond and the statement got lost when I felt his bony fingers between my already wet folds. Trailing along and spreading them with impatience and I could no longer contain my voice.  
The sensation stopped for just a moment before shifting and I felt something bigger and hotter press against my core. I felt his breath linger on my lips as he pecked and I opened my eyes. Sans grinned down at me, eyes filled with desire, I wondered if I looked the same. 

Sitting up he gripped my hips tighter quickly burying his length into me with few harsh thrusts. I heard myself scream with pleasure, I felt my walls throbbing around him. With no more time to waste he began thrusting, each one short, yet strong, his pace quick. My arms shot up without my demand wrapping around his neck as I pulled him closer. He followed my movements, a bit too eagerly, his hands trailed on my back and he pressed me against him. I felt him reach deeper and it felt divine. 

I don't know how much time had passed, it felt like hours and at the same time like moments. My mind was a mess, I was only occasionally brought back to reality when my palms hurt too much from my own grip. As I held my moans back a little more I heard the sounds now filling the usually quiet room. The creaking of a large bed, sheets moving underneath us, the sound of wet flesh and my heartbeat. Somehow my heartbeat was the loudest sound, ringing clearly in my ears and my head quicker than I thought was possible.

I heard his breath hitch, as my back arched in release. Stopping for a moment he cupped my face leaning closer and our lips bushed. I kissed him back trying to match with his passion. My mouth opened for him almost immediately, his tongue slipped in. It battled against mine easily overpowering me, it explored every part of my mouth, licked ever inch. Only an hour ago it would've sounded disgusting to me, but now it was just right.  
I chuckled into his mouth as a thought crossed my mind. Moments later we pulled away gasping for air.  
"What's so funny?" - He asked through a sly grin.  
"I just realized something. We kissed for the first time _after_ we had sex"  
Now it was his turn to laugh - "after? Nah, love. During" - he gave me one more small peck on my lips before picking up his pace once again - "we're far from over"  
I'd never admit, but I was hoping for that. 

He sat up, my hips firmly held between his hands as his movements became stronger and faster then before. I gripped onto the sheets unable to keep my body still and my cries muted, it felt too good. He seemed pleased with my reaction and his thrusts turned a bit softer, less chaotic. Sans shuddered pushing my hips against him as hard as he could reaching deeper. I felt something warm and sticky leak inside of me. He remained in that position few more seconds grinning at me like the world was his.

______  
He wasn't kidding when he said we weren't over. Right after he was done he gently hugged me, still completely sheathed in me. I only remembered his deep voice whispering to me "ready for the second round?". I didn't even have time to nod what he started to move again. Through the night his pace only quickened. Though with each 'new round' he seemed to be rougher it didn't hurt, it felt better. 

Hours had passed when we finally settled down, both too exhausted to move any more. I was cuddled in his chest, while his arms were wrapped around me protectively as he tried to heal my sour muscles claiming that it was his fault. It really was, so I let him.  
Inching closer to sleep I let my thoughts arrange themselves. That's when I remembered something that seemed insignificant to me before.

"Sans" - I called out through sleep. He hummed tightening his grip around me - "what did you mean 'you were waiting'?"  
He let out another hum, this time a curious, or maybe, a confused one.  
"You said you were waiting for something when I got angry at you. You said I'll know soon, but I still don't"  
He laughed gently stroking my back - "I was waitin' for the right time" - after my unsatisfied groan he continued - "for yer... I think ya call it ovulation"  
I froze, sleep partially leaving me - "wait. Are you saying humans and monsters can... can have children? A-And.. you want... with me?" - I half whispered as if someone could hear.  
"Yap. You don't wanna?" - His voice fell in mixture of disappointment and fear.  
"I do" - I said instantly. I really did, I always did. That alone was enough for me to not get mad at his irresponsible act. He let out a sigh of relief - "just warn me next time" 

"Heh, sure thing"  
"What?"  
I looked up at him only to be greeted with a wide shit eating grin. It took me bit to process what I said. My face went completely red and I tried to hide it in his chest. He let out the laugh he was so obviously holding back, actually helping me. He covered my head with one arm, successfully hiding it from everything outside while the other held a firm grip on my waist.

"S...So when would we know if it worked?" - I asked building up the courage.  
Silence. Shouldn't I have asked that?

"Love, there's a tiny Soul in ya" - As he spoke my hand reached down and I slowly stroke my stomach stopping a bit lower. Was he serious?

"It's bright and kind. Just like it's mother's"


End file.
